Remediation of Metal-Contaminated Soil by an Integrated Soil Washing-Electrolysis Process
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Soil and Sediment Contamination: AnInternational JournalPublication details, including instructions for authors andsubscription information:http://www.tandfonline.com/loi/bssc20
Remediation of Metal-ContaminatedSoil by an Integrated Soil Washing-Electrolysis ProcessShih-Hsien Chang a , Kai-Sung Wang a , Chung-Yih Kuo a , Chih-YuanChang a & Ching-Tung Chou aa Department of Public Health , Chung-Shan Medical University ,Taichung, Taiwan, ROCPublished online: 18 Jan 2007.
To cite this article: Shih-Hsien Chang , Kai-Sung Wang , Chung-Yih Kuo , Chih-Yuan Chang & Ching-Tung Chou (2005) Remediation of Metal-Contaminated Soil by an Integrated Soil Washing-ElectrolysisProcess, Soil and Sediment Contamination: An International Journal, 14:6, 559-569
To link to this article: http://dx.doi.org/10.1080/15320380500263758
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Soil & Sediment Contamination, 14:559569, 2005Copyright Taylor & Francis Inc.ISSN: 1532-0383 print / 1549-7887 onlineDOI: 10.1080/15320380500263758
Remediation of Metal-Contaminated Soil by anIntegrated Soil Washing-Electrolysis Process
SHIH-HSIEN CHANG, KAI-SUNG WANG, CHUNG-YIH KUO,CHIH-YUAN CHANG, CHING-TUNG CHOU
Department of Public Health, Chung-Shan Medical University, Taichung,Taiwan, ROC
Chelating agents such as EDTA and DTPA are often used to remove metals from soil.However, their toxicity, bio-recalcitrance, and problems with recovery of heavy metaland chelating agents severely limit their applications. A biodegradable chelating agent,LED3A, and two surfactants, SDS and Triton X 100, were evaluated as potential alter-natives for remediation of metal-contaminated soil.
LED3A alone only removed 40% of cadmium the addition of surfactant signif-icantly enhanced its cadmium removal capacity up to 80% for a wide range of pH(5 to 11). The enhancement increased with both surfactant concentrations and LED3Aconcentrations. Because LED3A had a much higher removal capacity for copper, thesynergistic effect of surfactant-LED3A mixture was less obvious. Sequential extractionanalysis indicated that the LED3A not only removed copper from carbonate and Fe-Mnoxide fraction, but also from organic fractions. A three-dimension electrolysis reactorcould effectively recover both metals and LED3A-SDS within thirty minutes. The com-bined soil washing by LED3A-surfactants and electrolysis provides a potential approachfor remediation of copper- and cadmium-contaminated soils.
Keywords Soil washing, sequential extraction, LED3A, electrolysis.
The presence of heavy metals in soil poses risks to health and the environment. Soil wash-ing is an inexpensive and practical technique for metal removal. The use of diluted acidscan dissolve soil matrix and damage soil physiochemical and biological properties (Baronaet al., 2001). Chelating agents such as ethylene diamine tetraacetic acid (EDTA) and di-ethylene trinitrilo pentaacetic acid (DTPA) have proven effective in removing metals fromsoils (Peters, 1999; Hong et al., 2002). Their biotoxicity, biorecalcitrance, and problemswith recovery of heavy metals and extracting agents from supernatant severely limit theirapplications (Hong et al., 2002).
Surfactants are amphiphilic molecules with a hydrophilic head group and a hydropho-bic tail group. Based on their hydrophilic head groups, surfactants can be divided into threecategories: anionic, cationic, and nonionic (Huang et al., 1997). Surfactants at low con-centrations exist as monomers and adsorb onto surfaces and interfaces. When surfactant
This study was supported by the National Science Council of Taiwan under contract NSC91-2211-E-040-001.
Address correspondence to S.-H. Chang, Department of Public Health, Chung-Shan MedicalUniversity, Taichung 402, Taiwan, ROC. E-mail: firstname.lastname@example.org
560 S.-H. Chang et al.
concentrations increase above a certain level (i.e. critical micelle concentration, CMC), themonomers aggregate to form micelles, which have a hydrophobic interior and a hydrophilicexterior (Haigh, 1996). Although anionic surfactants could increase heavy metal removalfrom soil, they are much less effective compared to chelating agents (Nivas et al., 1996;Doong et al., 1998; Gadelle et al., 2001). The information on interactions of chelatingagents and surfactants on soil metal removal is scarce.
Sequential extraction analysis can help identify the geochemical fractions of metalsin soil (Tessier et al., 1979). Basically, the more stable the metal binding is with the soil,the stronger extractants are required. Heavy metals in exchangeable and carbonate formsare easily solubilized by acids. In contrast, heavy metals bound to organic and crystallinelattice are difficult to extract (Gleyzes et al., 2002).
LED3A (Lauroyl-ED3ANa2, Dow company) is structurally similar to EDTA. It hypoth-esizes that LED3A should have a similar metal extractive capacity as that of EDTA. Thepresence of anionic surfactant (SDS) and nonionic surfactants (Triton X-100) may affect themetal extractive capacity of LED3A because it poses hydrophobic portion (lauryl functiongroup). In this study, the effects of extractants (surfactants, chelating agent, and surfactant-chelating agent mixture) on cadmium and copper removal at different soil solution pH wereinvestigated. Second, sequential extraction analysis was conducted to determine extractivecapacities of extractants to remove metal from different geochemical fractions. Finally,electrolysis was performed to recover metal from soil-washing solution. The objective ofthis study is to assess the feasibility of the integrated soil washing-electrolysis process formetal-contaminated soil remediation.
2. Materials and Methods
2.1 Soil Preparation
The soil was taken from a park on the Chung-Shan Medical University campus. It wassieved (90% purity, Sigma, USA), Na2EDTA2H2O (100% purity,Tedia, USA), and LED3ANa2 (30%, Hampshire Chemical Corp., USA) (Table 1). Toprepare the different extractants, first, two-fold desired concentrations of surfactant (orchelating agent) were prepared with distilled water. To prepare the desired surfactant-alone(or chelating alone) solution, the 20 ml of surfactant solution was mixed with 20 ml ofdistilled water. To obtain desired surfactant-chelating agent solution, 20 ml of 4, 0.4, 0.04,0.004, 0% of surfactants (SDS or Triton X-100) and 20 ml of 0.02, 0.01, 0.002, 0.001, and0 M of LED3A were mixed. The extractant solution was adjusted to desired pH by NaOH
Remediation of Metal-Contaminated Soil by Washing-Electrolysis Process 561
Table 1Properties of surfactants and chelating agent used in this study
Type Chemical formula MWCMC mM(mg L1)
Triton X 100 Nonionic surfactant C12H25O(CH2CH2O)4H 647 0.18 (268)1
SDS Anionic surfactant C12H25OSO2ONa 288 8.4 (2420)2
EDTA-Na2 Chelating agent C10H12N2Na2O82H2O 372.2 NA3LED3A-Na2 Anionic surfactant/ Lauroyl-ED3ANa2 459 4 (1700)4
1Edwards et al., 1994.2Deshpande et al., 1999.3Chelating agent, NA = not applicable.4Crudden et al., 1994.
or HNO3 solution. 40 ml of extractant was added into 5 g of metal-contaminated soil in apolyethylene centrifuge tube and mixed on a reciprocating shaker at 30 rpm for 3 hours.
The soil-washing supernatant was removed by centrifugation (1500 rpm, 30 min),filtered by a Whatman 42 filter paper (2.5m, Whatman, USA), and then analyzed byatomic absorbance spectrophotometry (AAS, Perkin-Elmer, model 3300). Distilled waterwas used to extract the residual extracting solution by following the same procedure, exceptthat the extracting period was shortened to one hour. All experiments were performed intri